history of earth

precambrian era

• moon very close to earth causing larger tides

• early precambrian has no O2 but oxygen increased later due to cyanobacteria (great oxidation event) -> oxygen toxic for many bacteria

cambrian period

• Cambrian explosion, 530 million years ago

• introduced most current marine invertebrate phyla, ozone layer fully formed

ordovician period

• first choradates (jawless fish) recorded

• first evidence of terrestrial life appeared, climate cooled

silurian period

• first jawed fish appeared

• two large landmasses/continents formed

• warm/wet climate

devonian period

• age of fishes, first bony fishes appeared,

• co2 decline and o2 increase because of proliferation of and plants

• mass extinction late in period

• emergence of tetrapods moving onto land

carboniferous period

• forest reptiles arose,

• amphibians radiated briefly

• extensive forests provided today’s coal beds

• increase atmospheric o2

Permian period

• continents arrived at their present positions

• oxygen increased to today’s level (21%)

• rapid diversification of mammals and birds

• angiosperms dominated

Neogene period

• more seasonal climate

• mammals adapted to cold, some moved north or south

• ice age began at the end and extended into the quaternary period

Quaternary period

• series of repeated glaciations

• evolution of homo-

• extiniction of large mammals